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    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
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    <title>Document</title>
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<body>
    <script>
        function point(m=1, n=1) {
            console.log(m + "+" + n + "=" + (m + n));
        }

        point(); //m=1,n=1,3
        point(100); //m=100,n=1
        point(200, 300); //m=200,n=300
        point(undefined, 400); //m=1,n=400
        point(500, undefined); //m=500,n=1
        point(0, 0); //m=0,n=0 这个结果正确的
    </script>
</body>

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